Although hypoxia and ischemia are generally considered to be the underlying causes of retinal neovascular diseases, previous inability to perform direct noninvasive measurements of retinal oxygen saturation and blood flow has limited understanding of both the pathogenesis of retinal neovascularization and the basis of the success of therapeutic panretinal photocoagulation. The Retinal Vessel Oximeter (RVO) that we have developed permits noninvasive measurement of the oxygen saturation of blood in retinal vessels. We propose to refine the RVO for clinical use and apply it to the study of oxygen saturation in retinal vessels of both normal subjects and diabetic patients without and with retinopathy. We will also determine, in the primate retina, the oximetric changes produced by either photocoagulation-induced branch vein occlusion or panretinal photocoagulation. The proposed human and primate studies may provide information important for understanding the pathophysiology of retinal neovascularization, and determine whether the diagnostic potential of retinal oximetry warrants more extensive clinical studies.